Cataract, a major cause of blindness in the world, develops as a result of age-related modifications and aggregation of the eye lens proteins. a-Crystallin accounts for nearly 40% of the adult lens proteins but its structure-function is yet to be fully understood. The chaperone-like activity of a-crystallin is believed to play a central role in maintaining lens transparency. We propose the following specific aims to increase our understanding of chaperone function of a-crystallin and its subunit organization to meet our long-term goal of understanding structure-function of a-crystallin. 1) Confirm that residues 70-88 in aA-crystallin and residues 73-92 in aB-crystallin are the major chaperone sites. Determine the amino acid sequences (binding site) in aB-crystallin that contribute to the enhanced hydrophobicity and chaperone function at 37[unreadable]C following deletion of 54-61 sequence. 2) Identify the a-crystallin binding site(s) in p- and y-crystallins during an in vitro chaperone assay at 37[unreadable]C. Identify the interaction sites in a-p and a-y complexes in human lens high-molecular-weight aggregates with the use of novel cross- linkers and mass spectrometric analysis. 3) Determine the directional preference and orientation of ADH peptide (YSGVCHTDLHAWHGDWPLPVK) during its interaction with aA- crystallin by site-directed fluorescence labeling and quenching studies. 4) Identify and characterize the aB-aB-;aB-aA- and aA-aA- crystallin interaction sites using cysteine scanning mutagenesis and chemical modification. We plan to accomplish these specific aims by site-directed mutagenesis studies and the use of novel cross-linkers and mass spectrometric methods. Understanding the structure of a-crystallin and its mechanisms of its action, including its interaction with other lens proteins, is likely to provide us better tools to delay or prevent cataractogenesis.